TSVs are signaling paths formed between a contact point on a first surface of the device and a contact point on a second surface of the device. Typically, but not always, the TSV signaling path will include or be coupled to circuitry within the device. TSVs are invaluable in the development and production of 3D stack die assemblies where signals pass vertically up and down the die in the stack. There can be thousands of TSVs in a die providing a large number of up and down signaling path ways in a 3D stack die assembly. TSVs may be used to pass uni-directional signals or bi-directional signals. Each of these thousands of TSV path ways must be tested to ensure the TSVs are capable of transferring signals at required electrical specifications. This disclosure describes a novel method and apparatus for testing signal TSVs in a die using a test circuit means for stimulating and analyzing one end of the TSV while the other end of the TSV is held at a known voltage potential, which, in this disclosure, is shown to be a ground voltage potential.